Polymeric foams can be generally classified as either closed-cell foams or as open-cell foams. Open-cell foams can be used as a matrix to contain various liquids and gases. They are capable of various industrial applications such as, for example, use as wipes and diapers, as carriers and ion exchange resins. For some of these applications, it is desirable to have porous crosslinked polymer blocks which have a very low density and a high capacity of absorbing and retaining liquids. Such high absorption capacity, low density, porous polymer blocks can be prepared by polymerizing a specific type of water-in-oil emulsion known as high internal phase emulsion (HIPE) having relatively small amounts of a continuous oil phase and relatively greater amounts of an internal water phase. Further, other properties such as thin dry thickness (i.e., thickness of the polymer product after removal of water) and low compressive strain (i.e., resistance to compression deflection) are also desirable for use as an absorbent.
Typically, these high absorption capacity, low density foams are prepared by forming a high internal phase water-in-oil emulsion (typical water to oil ratio of above 9:1) in the presence of a surfactant and polymerizing the monomers in the oil phase of the emulsion with a polymerization initiator at a temperature of around 60.degree. C. for about 8 hours. However, it has been found that at a higher water to oil ratio of above 30:1, the stability of the emulsion is poor, sometimes causing the emulsion to break.
It is therefore an object of the present invention to provide a water-in-oil high internal phase emulsion with improved stability at higher water to oil ratios. It is another object of the present invention to provide a process to prepare low density, porous, crosslinked, polymeric foams with improved absorption capacities and foam properties.